Chapter 7 Membrane Structure and Function PowerPoint Lectures for Biology Eighth Edition Neil Campbell and Jane Reece Fluid Mosaic Model Scientific Inquiry Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein Freeze fracture studies of the plasma membrane supported the fluid mosaic model Freeze fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer TECHNIQUE RESULTS Extracellular layer Knife Plasma membrane Proteins Inside of extracellular layer Cytoplasmic layer Inside of cytoplasmic layer The Fluidity of Membranes Lateral movement 107 times per second a Movement of phospholipids Flip flop once per month Proteins in the plasma membrane Can drift within the bilayer EXPERIMENT Researchers labeled the plasma membrane proteins of a mouse cell and a human cell with two different markers and fused the cells Using a microscope they observed the markers on the hybrid cell RESULTS Membrane proteins Mouse cell Human cell Hybrid cell Figure 7 6 Mixed proteins after 1 hour CONCLUSION The mixing of the mouse and human membrane proteins indicates that at least some membrane proteins move sideways within the plane of the plasma membrane The Fluidity of Membranes Fig 7 5b Fluid Unsaturated hydrocarbon tails with kinks b Membrane fluidity Viscous Saturated hydrocarbon tails The Fluidity of Membranes Cholesterol c Cholesterol within the animal cell membrane Fig 7 7 Fibers of extracellular matrix ECM Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE Fig 7 8 N terminus C terminus Helix EXTRACELLULAR SIDE CYTOPLASMIC SIDE Fig 7 9 Signaling molecule Enzymes ATP a Transport Receptor Signal transduction b Enzymatic activity c Signal transduction e Intercellular joining f Attachment to the cytoskeleton and extracellular matrix ECM Glycoprotein d Cell cell recognition Fig 7 10 ER 1 Transmembrane glycoproteins Secretory protein Glycolipid 2 Golgi apparatus Vesicle 3 4 Secreted protein Plasma membrane Cytoplasmic face Extracellular face Transmembrane glycoprotein Membrane glycolipid Fig 7 11 Molecules of dye Membrane cross section WATER Net diffusion Net diffusion Equilibrium a Diffusion of one solute Net diffusion Net diffusion b Diffusion of two solutes Net diffusion Net diffusion Equilibrium Equilibrium Fig 7 12 Lower concentration of solute sugar Higher concentration of sugar H2O Selectively permeable membrane Osmosis Same concentration of sugar Fig 7 13 Hypotonic solution H2O Isotonic solution H2O H2O Hypertonic solution H2O a Animal cell Lysed H2 O Normal Shriveled H2O H2O H2O b Plant cell Turgid normal Flaccid Plasmolyzed Filling vacuole 50 m a A contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm Contracting vacuole b When full the vacuole and canals contract expelling fluid from the cell Fig 7 UN3 Environment 0 01 M sucrose Cell 0 03 M sucrose 0 01 M glucose 0 02 M glucose 0 01 M fructose Fig 7 UN4 Water balance in cells with walls H2O Turgid normal H2O H2O Flaccid H2O Plasmolyzed EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM a A channel protein Carrier protein b A carrier protein Solute Fig 7 16 7 EXTRACELLULAR FLUID Na high K low Na Na Na Na Na Na Na Na CYTOPLASM Na Na low K high P ADP 2 1 ATP P 3 K K K K K P K 6 5 4 P Fig 7 17 Passive transport Active transport ATP Diffusion Facilitated diffusion Fig 7 18 ATP EXTRACELLULAR FLUID H H Proton pump H CYTOPLASM H H H Fig 7 19 ATP H H Proton pump H H H Sucrose H cotransporter H H Diffusion of H H Sucrose Sucrose Three types of endocytosis In phagocytosis a cell engulfs a particle by Wrapping pseudopodia around it and packaging it within a membraneenclosed sac large enough to be classified as a vacuole The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes PHAGOCYTOSIS EXTRACELLULAR CYTOPLASM FLUID Pseudopodium 1 m Pseudopodium of amoeba Food or other particle Bacterium Food vacuole Food vacuole An amoeba engulfing a bacterium via phagocytosis TEM In pinocytosis the cell gulps droplets of extracellular fluid into tiny vesicles It is not the fluid itself that is needed by the cell but the molecules dissolved in the droplet Because any and all included solutes are taken into the cell pinocytosis is nonspecific in the substances it transports Figure 7 20 PINOCYTOSIS 0 5 m Plasma membrane Pinocytosis vesicles forming arrows in a cell lining a small blood vessel TEM Vesicle RECEPTOR MEDIATED ENDOCYTOSIS Coat protein Receptor Coated vesicle Ligand Coated pit A coated pit and a coated vesicle formed during receptormediated endocytosis TEMs Coat protein Plasma membrane 0 25 m You should now be able to 1 Define the following terms amphipathic molecules aquaporins diffusion 2 Explain how membrane fluidity is influenced by temperature and membrane composition 3 Distinguish between the following pairs or sets of terms peripheral and integral membrane proteins channel and carrier proteins osmosis facilitated diffusion and active transport hypertonic hypotonic and isotonic solutions Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings 4 Explain how transport proteins facilitate diffusion 5 Explain how an electrogenic pump creates voltage across a membrane and name two electrogenic pumps 6 Explain how large molecules are transported across a cell membrane Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings
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